微波辅助木质素脱甲基化改性及结构表征

Preparation and Characterization of Demethylated Lignin Assisted by Microwave Irradiation

为提高木质素的反应活性,采用微波辅助加热方式,在HBr/十六烷基三正丁基溴化磷(HBr/TBHDPB)体系下对木质素进行脱甲基化改性。考察了HBr用量、反应温度、反应时间和催化剂用量对木质素改性反应的影响。通过紫外光谱(UV)、核磁共振氢谱(1H NMR)、傅里叶变换红外光谱(FT-IR)、凝胶渗透色谱(GPC)和元素分析等手段研究了木质素改性前后的官能团及分子质量变化,并由羟甲基化反应和曼尼希反应分析了木质素改性前后的活性变化。结果表明:木质素在微波辅助加热条件下,HBr用量为20 mmol/g,催化剂TBHDPB用量为木质素质量的2%,95℃反应1 h,制备的改性木质素含酚羟基为4.95%,相比原料木质素提高了32.71%,甲氧基为6.11%,相比原料木质素降低了20.44%。与甲醛反应的活性提高了18.15%,胺基侧链增加了7.54%。UV、1H NMR和FT-IR分析也表明,改性木质素的酚羟基含量增加,甲氧基含量降低。

In order to improve the reaction activity of lignin,the demethylation modification was carried out with aid of microwave heating in the presence of hydrobromic acid and（ HBr）-hexadecyltributylphosphonium bromide（ TBHDPB）. The effects of HBr dosage,temperature,time and dosage of catalyst TBHDPB on reaction were investigated. Structural and molecular weight of starting purified lignin and modified lignin were characterized by ultraviolet spectrum（ UV）,nuclear magnetic resonance hydrogen spectrum（^1H NMR）,Fourier transform infrared spectroscopy（ FT-IR）,gel permeation chromatograph（ GPC） and elemental analysis. The reaction activities of lignin before and after modification were evaluated by hydroxymethylation and Mannich reaction.The results showed that the content of phenolic hydroxyl group of modified lignin was 4. 95%,which increased by 32. 71%. When the acid reacted with the purified lignin at the dosage of 20 mmol / g at 95 ℃ for 1 h with TBHDTB（ 2% to Lignin） under microwave irradiation,the content of methoxyl group was 6. 11%,which decreased by 20. 44%. The reaction activity withformaldehyde increased by 18. 15%,whereas the amino side chain increased by 7. 54% compared with the starting lignin. The analyses of UV,^1H NMR and FT-IR confirmed the increase of the contents of phenolic hydroxyl group and methoxyl group.